order for it to maintain constant brightness, thus requiring the peak current to increase proportionally. This causes a number of issues that limit the practical size of a Charlieplexed display. LEDs often have a maximum peak current rating as well as an average current rating. If the microcontroller code crashes, and a one-led-at-a-time Charlieplex is being used, the single LED left lit is under much higher stress than it would be in a row-at-a-time Charlieplexed display or in a traditionally multiplexed display, increasing the risk of a failure before the fault is spotted. Requirement for tristate All the outputs used to drive a Charlieplexed display must be tristate. If the current is low enough to drive the displays directly by the I/O pins of the microcontroller, this is not a problem, but if external tristates must be used, then each tristate will generally require two output lines to control, eliminating most of the advantage of a Charlieplexed display. Since the current from microcontroller pins is typically limited to 20 mA or so, this severely restricts the practical size of a Charlieplexed display. However, it can be done by enabling one segment at a time. Complexity Charlieplex matrices are significantly more complicated, both in the required PCB layout and microcontroller programming, than using prebuilt multiplex matrices. This increases design time. Soldering components can also be more time-consuming than for multiplexed LED arrays. A balance between complexity and pin use can be achieved by Charlieplexing several pre-built multiplexed LED arrays together. Forward voltage When using LEDs with different forward voltages, such as when using different color LEDs, some LEDs can light when not desired. In the diagram above it can be seen that if LED 6 has a 4 V forward voltage, and LEDs 1 and 3 have forward voltages of 2 V or less, they will light when LED 6 is intended to, as their current path is shorter. This issue can easily be avoided by comparing forward voltages of the LEDs used in the matrix and checking for compatibility issues. Or, more simply, using LEDs that all have the same forward voltage. This is also a problem where the LEDs are using individual resistors instead of shared resistors, if there is a path through two LEDs that has less LED drop than the supply voltage these LEDs may also illuminate at unintended times. LED failure If a single LED fails,